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Suggestions for fixturing a lot of round parts

The job in question is parts for a sign made in 6061. The fun part is that each sign consists of a 84 circles, in a swirl kind of like the arms of a galaxy. There are 12 "arms" and each one has seven circles ranging from about 2-3" diameter and 1/2" thick. So it's basically 7 unique parts, repeated 12 times. On the plus side, they're a simple 2-op top/bottom side job.

My plan was to do the first op to machine multiple round blanks from a single long rectangular bar, cut the blanks apart on the bandsaw, then pop them into a fixture to machine the rest of the material off and put a nice flycut finish on. My idea was to make a single fixture with one station for each of the 7 diameters (I think I will have enough table area) which seems like the most efficient solution.

My question is whether anyone has suggestions on the best way to go about fixturing these. Everything I've done in volume before has been rectangular so I could use the hexagonal-type fixture clamps. I have a bunch of those, but I don't see they'd be much use for grabbing onto something round, and no, I can't put a plat anywhere .

My first thought was the Uniforce clamps from Mitee-Bite, which run about $30 each for the smallest size that looks suitable. They could hold two parts, so I'd need at least 4, and they don't seem like they'd be reusable, unless I happened to be doing the same job again. $120 is not out of the question, but I was curious to see if anyone had any alternatives that were either cheaper, or more general-purpose.

Re: Suggestions for fixturing a lot of round parts

You mention 84 pieces for a sign but are you making multiple signs? If lots of signs a special fixture might make sense but for a single sign I wouldn't bother.

I would probably cut the circles from a bar as you suggested. First face the bar with your flycutter, cut the disks but leave 3-4 tabs to keep the slugs in place, chamfer, cut the slugs apart on your bandsaw, clamp each slug in the vise supported on suitable thickness piece of scrap and using a pair of V-blocks. Face the back side to remove all traces of the tabs. If you could get away with slightly thinner than 1/2-inch you could leave tabs 25 thou thick and use 1/2-inch bar stock.

For this sort of low precision job I frequently support the aluminum on strips of MDF to avoid damage to the mill table and secure things with strap clamps.

Re: Suggestions for fixturing a lot of round parts

One sign consists of 84 pieces . Will definitely make one sign, depending on how it turns out, might be demand for two more copies.

This is paid, so I can pass fixture costs along, but still prefer to keep them low and/or reusable for other jobs. If it was 5-10 pieces I'd do it in the vise, but at this quantity I've found fixtures that pile on the parts really save time, especially if there are tool changes.

Re: Suggestions for fixturing a lot of round parts

7 diameters... just need a set of reversible long length vise jaws. 4 patterns on one side, 3 on the other. Machine the parts in that same 4 and 3 pattern out of solid bar, then just flip the bar and put it in the vise jaws and face off the whole set of 4 or 3 at one time. Less sawing and no tabs. No expensive mitee bite clamps either.

Re: Suggestions for fixturing a lot of round parts

I would still do it in the vise and then flip them and use V-blocks like kstrauss said. I would do it different though and buy 5/8" thick, 3" wide bar stock. Cut that into 3" lengths and put two in the vise at a time...one on each side. That will allow you to cut and chamfer any size circle up to 3" without making any fixtures. Then flip them over onto the V-blocks and machine the back sides.

I know fixtures save time, but a job this simple could be half done before you even get the fixture made.

Re: Suggestions for fixturing a lot of round parts

C*H*U*D's suggestion would work great using Talon jaws. However, I'm a tightwad!. My suggestion of using tabs would probably allow the use of 1/2-inch stock which is 80% of the cost of 5/8-inch plus I have 1/2-inch in inventory; I'd have to order in the 5/8 stock.

Re: Suggestions for fixturing a lot of round parts

Talon jaws wouldn't be necessary. You'd have enough stock to hold the blocks secure, even if you machined your parallels into a set of soft jaws. .1" would be more than enough which would allow facing on both sides.

But I did have to chuckle when you said you had 1/2" in inventory, since I'm writing this with a 3" X 5/8" X 6' piece of bar stock sitting next to my desk. I'd have to order the 1/2" stock :-)

Re: Suggestions for fixturing a lot of round parts

If your finished part is 1/2 inch thick, I would start with 3/4 inch material, machine some soft jaws to hold 3/16 of your material, cut your circles then flip the part over and cut the extra material off.

You can buy GOOD PARTS or you can buy CHEAP PARTS, but you can't buy GOOD CHEAP PARTS.

Re: Suggestions for fixturing a lot of round parts

Man, you guys have a lot higher tolerance for standing in front of the machine than I do! I'm going to want at least two, possibly three tools on the back side, so if I'm doing these one at a time I'm probably spending at least two minutes per part not making chips (manual tool change, no PDB), close to three hours just for that. If I can get seven parts at a time on the table, then I'm spending 15 minutes changing tools. But, I digress....

I do have a table-mountable 3-jaw chuck I use when making one-offs, and if I used that and a v-jaw in the vise I could cut tool change time in half at least, and spend a lot less time/money on fixtures. And I do have a set of Talon-Grip jaws so I could do blanks two at a time. I still have an idea in my head for a fixture that could fit everything (blank and finish) on the table at once, but might not be worth the time to design and make for the number of parts. We'll see as I work my way towards this...

Re: Suggestions for fixturing a lot of round parts

I hate changing tools as much as anyone but I'm also realistic and I have a PDB.

Designing and making a proper fixture would probably take me several hours or maybe even all day since I work slowly. I would need some stock ($$) for the fixture and maybe even some Mitee-Bite goodies. Debugging the CAM might ruin ($$) a few pieces of stock before I got everything right. You mentioned 3 hours of tool change time which, even with the best fixture, would not be zero. I don't see how a fancy fixture could be cost effective unless the job is repeated frequently.

Your suggestion of using a table mounted 3-jaw chuck would be preferable to my earlier comment about using a V-block in your vise.

Re: Suggestions for fixturing a lot of round parts

I Make all my fixtures drop into my vises for easy alignment and removal. It also gets the fixture up off the table to reach the part with short tools. I have 2 Kurt D688 vises. I'll take a 20+" piece of bar stock and make a soft jaw that spans across both vises. Machine the vise mounting holes on both bars. Mount the bar on the back non movable jaws on both vises. For the front movable jaws, I make the same part and cut a slit down the middle with my band saw so you can tighten each vise independently of course. Then I clamp the jaws together and machine/face profiles for whatever I'm holding.